The Danfoss FQS series is a robust paddle-type flow switch designed for reliable flow monitoring in liquid systems. It is commonly used in refrigeration systems, pumps, condensers, boilers, and various industrial equipment where accurate flow/no-flow detection is critical for system protection and control.

Working Principle

The FQS flow switch operates on a simple mechanical vane principle. When the liquid flow rate exceeds the adjustable set point, the fluid displaces a paddle (vane) mounted inside the pipe. This movement actuates a built-in SPDT microswitch, which changes its contact state to signal flow presence. When flow drops below the set point, the paddle returns to its resting position, and the switch resets.

Key Features

• Wide Flow Adjustment Range: The switch is adjustable for pipe sizes from DN25 to DN150 (1" to 6"). The paddle can be trimmed to suit specific pipe diameters, providing flexibility for various installations.
• High Pressure and Temperature Capability: Rated for working pressures up to 9.8 bar (142 psi) and media temperatures from -5°C to +80°C, making it suitable for demanding industrial environments.
• SPDT Microswitch Output: Provides a single-pole, double-throw (SPDT) contact rated at 15(8) A, 24-250 V AC, capable of directly controlling pumps, valves, or alarms.
• Robust Construction: Available with copper or stainless steel paddles, and a regular housing rated IP20 for indoor installation.
• Multiple Approvals: CE and UKCA certified, ensuring compliance with European safety standards.

Technical Specifications

• Flow Adjustment Ranges (Water):
  • DN25 (1"): Decreasing 18-45 L/min, Increasing 21-50 L/min
  • DN32 (1-1/4"): Decreasing 43-100 L/min, Increasing 46-102 L/min
  • DN40 (1-1/2"): Decreasing 63-140 L/min, Increasing 68-145 L/min
  • DN50 (2"): Decreasing 50-250 L/min, Increasing 58-255 L/min
  • DN65 (2-1/2"): Decreasing 105-565 L/min, Increasing 120-570 L/min
  • DN80 (3"): Decreasing 100-850 L/min, Increasing 115-880 L/min
  • DN100 (4"): Decreasing 200-940 L/min, Increasing 210-950 L/min
  • DN125 (5"): Decreasing 350-1120 L/min, Increasing 380-1140 L/min
  • DN150 (6"): Decreasing 530-1700 L/min, Increasing 570-1800 L/min
• Media Compatibility: Fresh water, glycol, neutral brine, and other non-corrosive liquids.
• Process Connection: 1" R thread (ISO 7-1).
• Electrical Connection: Screw terminals.
• Mounting Orientation: Horizontal or vertical (recalibration may be required for vertical installation).

Applications

The FQS series is ideal for flow/no-flow detection and pump protection in a wide range of industries, including:

• Refrigeration systems (evaporators, condensers).
• Pump dry-run protection and cooling water monitoring.
• Boiler flow control and heat exchanger monitoring.
• Water treatment and industrial process control.
• Heating and air conditioning systems (HVAC).